Electronegativity and Polarity

 Describe how electronegativity is used to determine bond type.  Compare and contrast polar and nonpolar covalent bonds and polar and nonpolar molecules.  Generalize about the characteristics of covalently bonded compounds.

 the relative ability of an atom to attract electrons in a chemical bond

 This table lists the character and type of chemical bond that forms with differences in electronegativity. 1.9

 Unequal sharing of electrons results in a polar covalent bond.  Bonding is often not clearly ionic or covalent.

 This graph summarizes the range of chemical bonds between two atoms.

 Polar covalent bonds form when atoms pull on electrons in a molecule unequally.

 Electrons spend more time around one atom than another resulting in partial charges at the ends of the bond called a dipole.

 Covalently bonded molecules are either polar or non-polar.  Non-polar molecules are not attracted by an electric field.  Polar molecules align with an electric field.

 Compare H 2 O and CCl 4  Bond polarity?  Shape?  Molecular Polarity?

Note: If bonds are polar, asymmetrical molecules are polar and symmetrical molecules are nonpolar.

 Solubility is the property of a substance’s ability to dissolve in another substance.  Polar molecules and ionic substances are usually soluble in polar substances.  Non-polar molecules dissolve only in non- polar substances.

 Covalent bonds between atoms are strong, but attraction forces between molecules are weak.  The weak attraction forces are known as van der Waals forces.  The forces vary in strength but are weaker than the bonds in a molecule or ions in an ionic compound.

 The force between two oppositely charged ends of two polar molecules is a dipole-dipole force.

 A hydrogen bond is an especially strong dipole-dipole force between a hydrogen end of one dipole and a fluorine, oxygen, or nitrogen atom on another dipole.

 Many physical properties are due to intermolecular forces.  Weak forces result in the relatively low melting and boiling points of molecular substances.

 Many covalent molecules are relatively soft solids.  Molecules can align in a crystal lattice, similar to ionic solids but with less attraction between particles.

 Solids composed of only atoms interconnected by a network of covalent bonds are called covalent network solids.  Quartz and diamonds are two common examples of network solids.